Pneumatic holding or clamping device

ABSTRACT

A holding or clamping device of the type comprising two pressure cylinders adapted to produce a first preliminary weak holding force and subsequently a greater holding force is provided with a sensor pin adapted to bring about a switch over from operation of the first cylinder to the second cylinder. The sensor pin is so loaded that it will only bring about the switching over when it strikes a hard object such as metal but is not actuated when it comes into contact with the human hand. The valve on actuation by the sensor pin closes the connection between the two chambers of the principal cylinder, which is constantly acted upon by pressure, and vents the rear side of the principal piston simultaneously.

Mayer Nov. 4, 1975 PNEUMATIC HOLDING OR CLAMPING DEVICE [76] Inventor:Max Mayer, 7914 Pfuhl 2 (Burlafingen), Germany [22] Filed: May 20, 1974[21] Appl. No.: 471,581

[30] Foreign Application Priority Data May 30, 1973 Germany 2327753 [52]US. Cl. 269/23; 91/416; 91/422; 100/53 [51] Int. Cl. B25B 1/18; FOlB15/02 [58] Field of Search 269/23, 25, 27; 100/53,

100/269 R, 269 B; 91/209, 404, 416, 422; 425/151,l53, 154

[56] References Cited UNITED STATES PATENTS 2,693,752 11/1954 Garapolo100/269 R 2,805,447 9/1957 Voges 91/209 X 3,554,087 1/1971 Florjancic91/404 Primary Examiner-Roy Lake Assistant ExaminerNeil Abrams Attorney,Agent, or FirmOstrolenk, Faber, Gerb &

Soffen [57] ABSTRACT A holding or clamping device of the type comprisingtwo pressure cylinders adapted to produce a first preliminary weakholding force and subsequently a greater holding force is provided witha sensor pin adapted to bring about a switch over from operation of thefirst cylinder to the second cylinder. The sensor pin is so loaded thatit will only bring about the switching over when it strikes a hardobject such as metal but is not actuated when it comes into contact withthe human hand. The valve on actuation by the sensor pin closes theconnection between the two chambers of the principal cylinder, which isconstantly acted upon by pressure, and vents the rear side of theprincipal piston simultaneously.

7 Claims, 1 Drawing Figure US. Patent Nov. 4, 1975 3,917,248

PNEUMATIC HOLDING OR CLAMPING DEVICE BACKGROUND OF INVENTION The presentinvention relates to a pneumatic holding or clamping device.

REFERENCE TO RELATED APPLICATION The present specification describes afurther development of the invention described in the specification ofmy U.S. Pat. No. 3,811,667.

This previous patent specification refers to a pneumatic holding orclamping device for holding workpieces and comprising two holdingcylinders with different diameters, of which the first cylinder with thesmaller diameter is adapted to bring about a preliminary advancingmovement, while the second or principal holding cylinder and which has agreater diameter than the first cylinder is adapted to produce a holdingforce at the end of the preliminary movement brought about by the firstcylinder, the holding force of the second cylinder being greater thanthat of the first cylinder and an abutment sensor being provided adaptedto open a valve for placing the second cylinder under pressure. Thesensor, which is preferably constructed as a pin which slides in apressing plate, ensures that the valve bringing about the switching overfrom. the smaller advancing force to the greater holding force can onlybe actuated when a hard article or object is detected, for example aworkpiece of metal, wood or the like, while the switching over to thefull clamping force is prevented reliably when a soft object as forexample the human hand is placed in the way of the sensor by mistake.The hand can therefore not be squashed by the high, dangerous holdingpressure.

Since all parts which are necessary for the function of the cylinder areincorporated in the latter, it can be connected directly with acompressed air line just like any other conventional holding or clampingcylinder.

The valve between the first cylinder and the clamping cylinder isarranged in accordance with the construction described in theabove-mentioned patent specification that on opening the valve thesensor ensures the transmission of the pressure within the firstcylinder to the rear side of the main piston. The transfer is carriedout in this case by the annular channel between the first cylinder whichis constructed with two walls.

SUMMARY OF INVENTION The present invention relates to a furtherdevelopment of the valve arrangement actuated by the sensor pin and oneof its objects is to construct the holding or clamping device in asimpler manner mechanically while keeping to a satisfactory and rapidfunction.

This aim is to be attained in accordance with the invention in the caseof a pneumatic holding or clamping device in accordance with theabove-mentioned patent specification by adopting the feature that thevalve actuated by the sensor pin closes, on actuation of the valve, theconnection between the two chambers of the principal cylinder and ventsthe rear side of the principal piston so that the pressure actingconstantly on the principal piston can become effective simultaneouslywith the venting of the rear side in order to close apply the clampingdevice. The pressure medium in this case does not need to pass throughany chokes or restrictions in the valve or the ducting and canimmediately become effective when venting takes place, some- 2. thingwhich can easily be carried out via an annular channel between the firstcylinder and a piston rod connected with the sensor.

In accordance with a further embodiment of the invention there is theprovision of two or more abutmentsensors which must be actuated jointlyand simultaneously in order to cause the clamping device to become fullyeffective. By the use of suitable see-saw arrangements it is possible totake account this requirement, the see-saw or rocking lever means thenbeing arranged to act upon the valve means.

DESCRIPTION OF PREFERRED EMBODIMENTS I In what follows an embodiment ofthe invention will be described with reference to the accompanyingdrawing. The single FIGURE of the drawing shows a sectional view of apneumatic clamping device constructed in accordance with the invention;

The clamping or holding device comprises a front housing part 10, whichserves for attachment to a holding rod 12. This housing part 10 guides acylinder 14 so that the latter can move longitudinally. The cylinder 14forms a hollow piston rod for the principal or main holding piston 18,which runs in a principal holding or clamping cylinder 20 connected withthe housing 10. The cylinder 20 is connected with a cylinder end plateor lid 22. The principal holding piston 18 engages a return spring 26,constructed in the form ofa compression helical spring, on the frontpart 10 of the housing. The rear side of the principal holding piston 18is continuously put under pressure via the axial inlet opening 23.Within an annual hole of the principal holding piston 18 a valve body 32can move axially and it has a rear sealing disc 17 and a front sealingdisc 19. The rear sealing disc 17 cooperates with a valve annular seat25 of the principal holding piston 18 and the front seal 19 cooperateswith the rear end of the first cylinder 14. The valve body 32 isprovided with a guide sleeve 27, which can be moved axially on a pin 29.This pin 29 is provided with a screw thread and screwed into an axialhole 31 in a push rod 24. The rod 24 is guided for sliding movement inthe cylinder 14 leaving an annular gap 33. At the top end this annulargap 33 is terminated by a seal 45 between the cylinder 14 and the piston24. Underneath there is the annular gap 33 which is connected via radialventing holes 35 with the atmosphere. The valve body 32 is supported bya nut 37 screwed onto the pin 29 and between the valve body 32 and therear end annular face of the piston 24 there is a helical compressionspring 39, which biases the valve body 32 to the rear. The push rod 24carries a sensor pin 52, which can be moved axially in a hole 50 of apressure plate 48 and the pressure plate is mounted on the front part ofthe cylinder 14 so as to be able to perform a limited swinging movement.A helical compression spring 56, which rests on an annular end face ofthe cylinder 14 and, respectively, on aring 55 mounted on the piston,presses the sensor pin 52 into its front terminal position, which isdefined by the sealing ring 19 on the rear annular end face of thecylinder 14. In this respect the sensor pin extends by a slight amountbeyond the front plane of the pressure plate 48.

The function of the holding or clamping device is as follows: Thecompressed air flows through the hole 23 at the upper cylinder end plate22 into the rear cylinder chamber 42. In the rest position representedin the drawing the valve disc of valve body 32 is raised from its seat25 and the valve body 32 has the valve disc 19 14, the rod 14 being sodimensioned that it overcomes the resistance of the compression spring26 and slowly advances the pressure plate 48 with a slight degree offorce. When the sensor pin 52 has run up against hard material, thevalve body 32 is displaced axially to the rear so that the sealing ring19 is raised and the sealing ring 17 comes into engagement with its seat25. As a result the air path between the front and the rear parts of theprincipal cylinder chamber is blocked and the pressure supplied via thehole 23 becomes fully effective on the principal holding piston 18 sothat the latter can move suddenly and with a large degree of forceforward because the front cylinder chamber can be vented via the valveopening between the ring 19 and the annular end face of the cylinder 14,the annular gap 33 and the radial holes 35 suddenly. Owing to theventing of the front cylinder chamber the principal holding piston 18reaches its full thrust force. The compression spring 39 arrangedbetween the valve body 32 and the sensor pin 52 extended via the rod 24brings about a resilient yielding of the valve body so that even afterwear of the seals on the valve plunger reliable closing of the hole orbore on the piston is ensured.

The compression spring 56 on the underside of the sensor pin 52 has thepurpose of holding the vavle body 32 reliably on its seat at the end ofthe cylinder 14 and to cause the sensor pin 52 to extend somewhat beyondthe pressure plate 48. The diameter of the valve plate of the valve body32 is so selected that the valve body is pressed before the switchingover operation sufficiently forcibly against the seat at the end of thecylinder l4 and it requires something more than a gentle force to pressin the sensor pin. The diameter of the valve plate accordinglydetermines the counter-pressure, which is necessary for actuating thesensor pin.

1 claim:

1. A pneumatic holding device for workpieces, comprising:

a first holding cylinder of narrower cross-section; a

first chamber defined in andby said first cylinder; a vent from saidfirst chamber;

a second cylinder of larger cross-section; a first piston sealinglylocated in and movable along and through said second cylinder; saidfirst piston dividing said second cylinder into second and thirdchambers;

a first conduit across said first piston and communi cating between saidfirst and said second chambers; a second conduit across said firstpiston and com- 4 municating between said second and said thirdchambers; a fluid inlet to said third chamber;

a valve movable for selectively opening one of said i first and secondconduits while closing the otherof said first and second conduits, andvice versa;

an abutment sensor extending out of said pneumatic holding device andbeing connected with said valve for causing the aforesaid movementthereof, in a manner such that application of pressure to said abutmentsensor shifts said valve to close said second conduit.

2. The pneumatic holding device of claim 1, further comprising a secondpiston in and extending along said first cylinder, and having acrosssection less than said narrower cross-section of said firstcylinder, thereby defining said first chamber between said firstcylinder and said second piston; said abutment sensor being connectedwith said second piston for moving same; said valve communicating withsaid second piston thereby to be moved by movement of said secondpiston.

3. The pneumatic holding device of claim 2, wherein said first cylinderis positioned within said second cylinder.

4. The pneumatic holding device of claim 2, wherein I said valvecomprises a valve body and a valve chamber, said valve chamber beingformed in said first piston; said valve body being movable in saidvalve'chamber;

a first valve seat in said valve chamber; said first cyl-.

inder extending into and terminating at an end in said first piston;said first valve seat being near said first cylinder end;

a second valve seat in said valve chamber, locate opposite said firstvalve seat, and formed in said first piston; said valve closing saidsecond conduit when said valve body is against said second valve seatand opening said second conduit when said valve body is against saidfirst valve seat.

5. The pneumatic holding device of claim 4, further comprising acompression spring between said valve body and said second piston forforcing them in opposite directions.

6. The pneumatic hoding device of claim 5, further comprising acompression spring normally biasing said through said second cylinder.

* i =i i

1. A pneumatic holding device for workpieces, comprising: a firstholding cylinder of narrower cross-section; a first chamber defined inand by said first cylinder; a vent from said first chamber; a secondcylinder of larger cross-section; a first piston sealingly located inand movable along and through said second cylinder; said first pistondividing said second cylinder into second and third chambers; a firstconduit across said first piston and communicating between said firstand said second chambers; a second conduit across said first piston andcommunicating between said second and said third chambers; a fluid inletto said third chamber; a valve movable for selectively opening one ofsaid first and second conduits while closing the other of said first andsecond conduits, and vice versa; an abutment sensor extending out ofsaid pneumatic holding device and being connected with said valve forcausing the aforesaid movement thereof, in a manner such thatapplication of pressure to said abutment sensor shifts said valve toclose said second conduit.
 2. The pneumatic holding device of claim 1,further comprising a second piston in and extending along said firstcylinder, and having a cross-section less than said narrowercross-section of said first cylinder, thereby defining said firstchamber between said first cylinder and said second piston; saidabutment sensor being connected with said second piston for moving same;said valve communicating with said second piston thereby to be moved bymovement of said second piston.
 3. The pneumatic holding device of claim2, wherein said first cylinder is positioned within said secondcylinder.
 4. The pneumatic holding device of claim 2, wherein said valvecomprises a valve body and a valve chamber, said valve chamber beingformed in said first piston; said valve body being movable in said valvechamber; a first valve seat in said valve chamber; said first cylinderextending into and terminating at an end in said first piston; saidfirst valve seat being near said first cylinder end; a second valve seatin said valve chamber, located opposite said first valve seat, andformed in said first piston; said valve closing said second conduit whensaid valve body is against said second valve seat and opening saidsecond conduit when said valve body is against said first valve seat. 5.The pneumatic holding device of claim 4, further comprising acompression spring between said valve body and said second piston forforcing them in opposite directions.
 6. The pneumatic hoding device ofclaim 5, further comprising a compression spring normally biasing saidfirst piston in a direction away from said abutment sensor.
 7. Thepneumatic holding device of claim 6, further comprising a pressure plateconnected with and movable with said first piston; said abutment sensorprojecting through and being freely movable with respect to saidpressure plate, such that application of pressure to said abutmentsensor moves same inward of said pressure plate and closes said valvebody against said second seat, thereby venting said second chamberthrough said first chamber and permitting build up of pressure in saidthird chamber, thereby to shift said first piston through said secondcylinder.